The present invention relates to electron beam sources and, in particular, to electron beam sources utilizing micro-electro-mechanical-systems (MEMS) devices and to methods for making the same. The invention is particularly useful for electron beam displays and for x-ray imaging.
Display devices play important roles in modern information and entertainment technologies such as computer monitors and TVs. The resolution requirement for typical computer monitors and TV screens is relatively modest, as human eyes can not resolve images finer than xcx9c100 micrometers. For display devices that humans will see at closer distances, for example, head-mounted displays, camera viewfinders, or wearable personal computing devices, a much higher resolution on the order of xcx9c3 micrometers is required. These head-mounted displays allow the free use of hands, and are thus useful for a number of unique applications such as a mobile wearable computer, a head-mounted display for detecting land mines, virtual reality traveling, or remotely guiding mechanical repair or even a surgical operation.
To provide a two-dimensional e-beam source, parallel beam illumination has to take place simultaneously at many different locations on the surface to be exposed. Two-dimensional, x-y addressable array of electron field emission sources include the cold tip cathode array described by C. A. Spindt, C. E. Holland, A. Rosengreen, and I. Brodie, in xe2x80x9cField emitter array development for high frequency operation,xe2x80x9d J. Vac. Sci. Technol. B, vol. 11, pp. 468-473, 1993, and the nanotube field emission display cathodes described by W. B. Choi, et al. in xe2x80x9cCarbon-Nanotube Based Field-Emission Displays for Large Area and Color Applicationsxe2x80x9d, Journal of Information Display, Vol. 1, No. 1, p. 59, December 2000. In theory such arrays may be used to achieve simultaneous supply of various e-beams. However, it would be impractical to make each cold cathode structure sufficiently small (on the order of xcx9c10-1000 nanometers) to obtain a display with a 10-1000 nm resolution. Even if such a nanoscale cathode structure would be fabricated, the number of cathode cells and associated lead wires required for x-y addressing would be astronomical. To produce a two-dimensional e-beam array for a display size of 12xc3x9712 inch area, it would take about 1012xcx9c1014 cathodes and wire connections. The fabrication of display devices having xcx9c3 micrometer pixel display cell size, as compared to the present cell size of xcx9c100 micrometers or larger, would be significantly more complex and expensive. Accordingly it would be desirable to be able to design and fabricate such high resolution display devices by using industrially viable and inexpensive techniques.
In accordance with the invention, an electron beam source for exposing selected portions of a surface to electrons comprises a plurality of nanoscale electron emitters and, associated with each electron emitter, a directional control element to direct the emitter toward a selected portion of the surface. In a preferred embodiment, the emitters are nanotubes or nanowires mounted on electrostatically controlled MEMS directional control elements. An alternative embodiment uses electrode directional control elements.